1. Field of the Invention
The present invention relates to a musical tone generating apparatus of an electronic musical instrument, which generates various musical tones.
2. Prior Art
Conventionally, in the electronic musical instrument, musical tone is generated by a tone generator, and its amplitude is controlled on the basis of the envelope signal, or musical tone is filtered by a filter which has a variable frequency characteristics. Thus, the musical tone has a peculiar tone color of an acoustic musical instrument. Hereafter, typical conventional apparatuses will be described.
The first conventional apparatus is disclosed in U.S. Pat. No. 4,135,424 and is shown in FIG. 17. In FIG. 17, there is an envelope generator of an electronic musical tone generating apparatus, which consists of a subtractor SUB, a multiplier M, a gate GT, an adder ADD and a shift register SRG. In the envelope generator, first of all, a target data Sa of the envelope of the musical tone is set on the subtractor SUB. The subtractor SUB subtracts a present data Sb from the target data Sa; that is, it calculates a difference between the target data Sa and the present data Sb. However, the present data Sb is an amplitude of the musical tone at present, and the target data Sa is a desired amplitude of the musical tone after a certain time. The difference is supplied to the multiplier M, wherein it is multiplied by a certain coefficient Sc (which is the number between 0 and 1, for example, 2.sup.-8), and is supplied to the adder ADD through the gate GT. The adder ADD adds the difference and the present data Sb, and outputs to the shift register SRG. As a result, the shift register SRG outputs a new present data Sb. Thus, the above-mentioned operations are performed with fixed interval (i.e., timing clock CK), and then, the envelope approaches the target data Sa, gradually. Finally, the envelope, i.e., the present data Sb, reaches the target data Sa. Therefore, if it changes the target Sa the envelope of the musical tone would change with passing time. As a result, the musical tone has a peculiar tone color of acoustic musical instrument.
Next, in the second conventional apparatus, waveform data of envelopes of the musical tone are memorized in a waveform memory, previously. Then, the waveform memory is accessed by a counter, so that the waveform data are outputted as the musical tone (data). At such time, a count of the counter is subtracted or is added on the basis of a clock plus. And then, the waveform data, i.e., the envelope, are changed by the variable count, following which the musical tone is controlled by the envelope. The musical tone has a peculiar tone color.
Next, the third conventional musical tone generating apparatus is disclosed in Japanese Utility Model Application laid-Open No. 50-114319 as is shown in FIG. 18. In FIG. 18, an envelope circuit 2 generates an envelope signal in accordance with operation of a keyboard 1. Next, an open-close circuit 3 is opened or closed according to the envelope signal; thus, the musical tone in accordance with operation of the keyboard 1 is outputted from a musical tone source 4. Also, the musical tone is filtered by a voltage control filter (VCF) 5, in which its cut-off frequency is controlled by the envelope signal. Thus, the musical tone which has a peculiar tone color is amplified by an amplifier AMP, then is outputted through a speaker SP as musical sound.
In addition, the fourth conventional musical tone generating apparatus is disclosed in U.S. Pat. No. 4,843,938 shown in FIG. 19. In FIG. 19, plural filter parameters which designate a frequency characteristic of a digital-filter 7, used as a tone color controller, are memorized in a memory 9 previously, and are supplied to the digital filter 7 according to touch information from a keyboard 1, in each fixed interval (Frame). Therefore, a musical tone from a waveform memory 9 is filtered by the digital-filter 8 having a frequency characteristic which changes with elapsed time. As a result, the envelope of the musical tone changes variously in accordance with the frequency characteristic. This musical tone is supplied to the D/A converter 10, and outputted as musical sound by the sound system SD.
However, the above-mentioned conventional apparatuses as shown in FIG. 17, FIG. 18, FIG. 19, and the third apparatus, repeatedly read out the waveform data of the musical tone within the predetermined segment from the continuous tone waveform. The tone color is not varied smoothly at a time when the conventional apparatus begins to read out the tone waveform data at the front portion of the segment after reading out the musical tone waveform data at the end portion of the segment. For this reason, there is an unnatural portion heard in the generated musical tone.
The apparatuses have waveforms having various segment structures, or have various filter characteristics, so that, for example, it is necessary to provide a complicated enveloped generator, or to provide a large filter characteristic memory.